This application claims priority of Japanese Patent Application Nos. 11-278611 filed on Sep. 30, 1999 and 2000-066984 filed on Mar. 10, 2000, the entire contents of which are hereby incorporated herein by reference.
1. Field of the Invention
The present invention generally relates to a communication apparatus, and in particular relates to a telephone line interface between a facsimile and a copier, a printer, and/or a card MODEM or the like that has a facsimile function.
2. Discussion of the Background Art
Recently, communication standards adopted by European countries have been unified into the Common Technical Regulation 21 (hereinafter referred to as the CTR 21).
However, the characteristics of a direct current that flows through a network control section of a communication apparatus, e.g., a facsimile, are different from those of the conventional standard. Namely, a direct current is required to have nonlinear characteristics that arise due to limits on a direct current that flows through a direct current circuit.
Further, since communication standards adopted by many countries (excepting Europe) are not uniform, linear characteristics are required in several countries, and the direct current characteristics must be changed to those of a destination country.
Therefore, two different baseboards for generating direct currents with different characteristics are necessary in the network control section of communication apparatus when communication with another country that has adopted a different communication standard is performed. Namely, a network control unit having both a background direct current circuit which does not limit a direct current to a prescribed value and that having the direct current circuit for the CTR 21 use, i.e., which limits a direct current, should be provided.
Further, the characteristics of a network, except for external line network connections executed by a public exchanger based on the Post Telephone Telegram standard (hereinafter referred to as the PTT standard) of the country, are sometimes not based on the PTT standard of the applicable country.
Specifically, an internal line exchanger that operates with a constant current is included among internal line exchangers, such as a small business use internal exchangers (hereinafter referred to as a PABX), a home PABX, and large scale exchangers employed in a business as a private line.
When using such an internal line exchanger, it has been shown that it is impossible to form a network connection between a communication apparatus and an internal line exchanger if the communication apparatus operates at a current value in excess of the prescribed limit upon the direct current. This is because the network characteristic of the internal line exchanger generally depends upon the manufacturer.
Further, there are strict standards for parameters related to control operations of the general public line networks above and beyond other networks. However, parameters related to control operations of other networks can be, to a large degree, set in consideration of general-purpose uses. Thus, the above-mentioned current limitation is generally not applied in internal line exchangers.
For example, the Japanese Patent Application laid Open No. 8-335994 describes technology related to the above-mentioned apparatus. The technology changes the characteristics of the direct current based on a country by connecting resistors in parallel to a photo relay. Thereby, it is possible to generate a direct current in accordance with a standard of the telephone line of an applicable destination country using a direct current generating circuit with a simple construction.
However, the above-mentioned related technology can not generate a direct current that includes nonlinear characteristics that limit a current flowing through the circuit to a prescribed value. Further, it is not necessary (or, in some cases, desirable) to directly limit a current that flows through a circuit when controlling a network except when the network is the general public line network. This is thus a source of problems.
The present invention has been made in view of the above noted and another problems and one object of the present invention is to address and resolve such problems.
A further object of the present invention is to provide a novel communication apparatus including a network control unit configured to interface with a telephone line. The network control unit may include a direct current circuit configured to carry a loop state direct current, and an electrical characteristic changing device configured to change one or more electrical characteristics of the direct current circuit so that the one or more electrical characteristics of the direct current circuit complies with a communication standard adopted by the other communication apparatus.
In yet another embodiment, the one or more electrical characteristics may include a limit (to a prescribed value) on a loop state direct current flowing through the direct current circuit, as well as a lack of limits thereon.
In yet another embodiment, the one or more electrical characteristics may be a limit upon the direct current when communication with a prescribed foreign country occurs.
In yet another embodiment, the one or more electrical characteristics may be changed based on a designation of the foreign country.
In yet another embodiment, an electrical characteristic alternating device may be provided to selectively alternate one of a plurality of electrical characteristic with another in correspondence with a kind of communication used and/or desired.
In yet another embodiment, the kind of communication may include external line communication and internal line communication.
In yet another embodiment, the one or more electrical characteristics may be alternated with those of a direct current limiting mode when the communication is transmitted to and from an external line.
In yet another embodiment, a current limiting device may be provided in the direct current circuit to limit a direct current flowing through the direct current circuit to a prescribed value.
In yet another embodiment, a switching device may be provided to select either a direct current limiting circuit configured to limit a direct current to the prescribed value or a direct current non-limiting circuit configured not to limit the direct current.
In yet another embodiment, a display device may be provided to display a screen through which either a direct current limitation mode, where a loop state direct current is limited, or a direct current non-limitation mode, where a loop state direct current is not limited, is set and/or selected.
In yet another embodiment, a dial call-generating device may be provided for generating a dial pulse or a tone signal, and the direct current limit is removed when the dial pulse or the tone signal relates to a network other than the general public line.
In yet another embodiment, the direct current limit may be implemented only when a dialed number of the dial call-generating device includes a prescribed number representing external communication.
In yet another embodiment, a ringing signal detection device may be provided for detecting a ringing signal, and the switching device may be controlled to switch to a direct current non-limiting mode when a ringing wave detected by the ringing signal detection device indicates reception from a network other than the general public line.
In yet another embodiment, a parameter generating device may be provided to generate a parameter representing a limit on the direct current, and the parameter need not be generated and included in parameters related to the control of the network when communication is practiced via a network other than a general public line.
In yet another embodiment, the parameter is set using the setting switch or a screen provided in the communication apparatus.